Semiconductor device and a method for fabricating the same

ABSTRACT

In a method of manufacturing a semiconductor device, first and second gate structures are formed. The first (second) gate structure includes a first (second) gate electrode layer and first (second) sidewall spacers disposed on both side faces of the first (second) gate electrode layer. The first and second gate electrode layers are recessed and the first and second sidewall spacers are recessed, thereby forming a first space and a second space over the recessed first and second gate electrode layers and first and second sidewall spacers, respectively. First and second protective layers are formed in the first and second spaces, respectively. First and second etch-stop layers are formed on the first and second protective layers, respectively. A first depth of the first space above the first sidewall spacers is different from a second depth of the first space above the first gate electrode layer.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 15/870,649 filed Jan. 12, 2018, now U.S. Pat. No. 10,797,048, which is a divisional of U.S. application Ser. No. 15/141,476, filed Apr. 28, 2016, now U.S. Pat. No. 9,893,062, the entire content of each of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a method for manufacturing a semiconductor device, and more particularly to a structure and a manufacturing method for insulating layers over a gate electrode and source/drain regions.

BACKGROUND

With a decrease of dimensions of semiconductor devices, a self-aligned contact (SAC) has been widely utilized for fabricating, e.g., source/drain (S/D) contacts arranged closer to gate structures in a field effect transistor (FET). Typically, a SAC is fabricated by patterning an interlayer dielectric (ILD) layer, under which a contact etch-stop layer (CESL) is formed over the gate structure having sidewall spacers. The initial etching of the ILD layer stops at the CESL, and then the CESL is etched to form the SAC. As the device density increases (i.e., the dimensions of semiconductor device decreases), the thickness of the sidewall spacer becomes thinner, which may cause a short circuit between the S/D contact and the gate electrodes. Accordingly, it has been required to provide SAC structures and manufacturing process with improved electrical isolation between the S/D contacts and gate electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A shows an exemplary plan view (viewed from the above) illustrating one of the various stages of a sequential fabrication process of a semiconductor device according to one embodiment of the present disclosure. FIG. 1B shows an exemplary cross sectional view along line X1-X1 of FIG. 1A. FIG. 1C is an enlarged view of the gate structure. FIG. 1D shows an exemplary perspective view illustrating one of the various stages of a sequential fabrication process of a semiconductor device according to one embodiment of the present disclosure.

FIGS. 2-16 show exemplary cross sectional views corresponding to line X1-X1 of FIG. 1A illustrating various stages of the sequential fabrication process of a semiconductor device according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific embodiments or examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, dimensions of elements are not limited to the disclosed range or values, but may depend upon process conditions and/or desired properties of the device. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Various features may be arbitrarily drawn in different scales for simplicity and clarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. In addition, the term “made of” may mean either “comprising” or “consisting of.”

FIGS. 1A and 1B show one of the stages of a sequential fabrication process of a semiconductor device according to one embodiment of the present disclosure. FIG. 1A shows a plan (top) view and FIG. 1B shows a cross sectional view along line X1-X1 of FIG. 1A.

FIGS. 1A and 1B show a structure of a semiconductor device after metal gate structures are formed. In FIGS. 1A and 1B, metal gate structures 10 are formed over a channel layer 5, for example, a part of a fin structure. The thickness of the metal gate structures 10 is in a range from 15 nm to 50 nm in some embodiments. Sidewall spacers 30 are provided on sidewalls of the metal gate structure 10. The film thickness of the sidewall spacers 30 at the bottom of the sidewall spacers is in a range from about 3 nm to about 15 nm in some embodiments, and is in a range from about 4 nm to about 10 nm in other embodiments. The combination of the metal gate structure 10 and sidewall spacers 30 may be collectively referred to as a gate structure. Further, source/drain regions 50 are formed adjacent to or between the gate structures, and spaces between the gate structures are filled with a first interlayer dielectric (ILD) layer 40. In this disclosure, a source and a gate are interchangeably used, and source/drain (or S/D) may refer to one of or both of the source and drain.

FIG. 1C is an enlarged view of the gate structure. The metal gate structure 10 includes one or more layers 16 of metal material, such as Al, Cu, W, Ti, Ta, TiN, TiAl, TiAlC, TiAlN, TaN, NiSi, CoSi, other conductive materials. A gate dielectric layer 12 disposed between the channel layer 5 and the metal gate includes one or more layers of metal oxides such as a high-k metal oxide. Examples of metal oxides used for high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and/or mixtures thereof.

In some embodiments, one or more work function adjustment layers 14 are interposed between the gate dielectric layer 12 and the metal material 16. The work function adjustment layers 14 are made of a conductive material such as a single layer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC, or a multilayer of two or more of these materials. For the n-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSi and TaSi is used as the work function adjustment layer, and for the p-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC and Co is used as the work function adjustment layer.

The sidewall spacers 30 include one or more layers of insulating material such as a silicon oxide based material or a silicon nitride based material, including SiO₂, SiN, SiON, SiCN and SiOCN. The first ILD layer 40 includes one or more layers of insulating material such as silicon oxide based material such as silicon dioxide (SiO₂) and SiON.

The material of the sidewall spacers 30 and the material of the first ILD layer 40 are different from each other, so that each of these layers can be selectively etched. In one embodiment, the sidewall spacer 30 is made of SiOCN, SiCN or SiON and the first ILD 40 layer is made of SiO₂.

In this embodiment, fin field effect transistors (Fin FETs) fabricated by a gate-replacement process are employed.

FIG. 1D shows an exemplary perspective view of a Fin FET structure.

First, a fin structure 310 is fabricated over a substrate 300. The fin structure includes a bottom region and an upper region as a channel region 315. The substrate is, for example, a p-type silicon substrate with an impurity concentration in a range from about 1×10¹⁵ cm⁻³ to about 1×10¹⁸ cm³. In other embodiments, the substrate is an n-type silicon substrate with an impurity concentration in a range from about 1×10¹⁵ cm⁻³ to about 1×10¹⁸ cm³. Alternatively, the substrate may comprise another elementary semiconductor, such as germanium; a compound semiconductor including Group IV-IV compound semiconductors such as SiC and SiGe, Group III-V compound semiconductors such as GaAs, GaP, GaN, InP, InAs, InSb, GaAsP, AlGaN, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In one embodiment, the substrate is a silicon layer of an SOI (silicon-on-insulator) substrate.

After forming the fin structure 310, an isolation insulating layer 320 is formed over the fin structure 310. The isolation insulating layer 320 includes one or more layers of insulating materials such as silicon oxide, silicon oxynitride or silicon nitride, formed by LPCVD (low pressure chemical vapor deposition), plasma-CVD or flowable CVD. The isolation insulating layer may be formed by one or more layers of spin-on-glass (SOG), SiO, SiON, SiOCN and/or fluorine-doped silicate glass (FSG).

After forming the isolation insulating layer 320 over the fin structure, a planarization operation is performed so as to remove part of the isolation insulating layer 320. The planarization operation may include a chemical mechanical polishing (CMP) and/or an etch-back process. Then, the isolation insulating layer 320 is further removed (recessed) so that the upper region of the fin structure is exposed.

A dummy gate structure is formed over the exposed fin structure. The dummy gate structure includes a dummy gate electrode layer made of poly silicon and a dummy gate dielectric layer. Sidewall spacers 350 including one or more layers of insulating materials are also formed on sidewalls of the dummy gate electrode layer. After the dummy gate structure is formed, the fin structure 310 not covered by the dummy gate structure is recessed below the upper surface of the isolation insulating layer 320. Then, a source/drain region 360 is formed over the recessed fin structure by using an epitaxial growth method. The source/drain region may include a strain material to apply stress to the channel region 315.

Then, an interlayer dielectric (ILD) layer 370 is formed over the dummy gate structure and the source/drain region. After a planarization operation, the dummy gate structure is removed so as to make a gate space. Then, in the gate space, a metal gate structure 330 including a metal gate electrode and a gate dielectric layer, such as a high-k dielectric layer, is formed, so as to obtain the Fin FET structure shown in FIG. 1D. In FIG. 1D, parts of the metal gate structure 330, sidewalls 330 and the ILD layer 370 are cut to show the underlying structure.

The metal gate structure 330, sidewalls 330, source/drain 360 and the ILD layer 370 of FIG. 1D substantially correspond to the metal gate structures 10, sidewall spacers 30, source/drain regions 50 and first ILD layer 40, of FIGS. 1A and 1B, respectively.

FIGS. 2-16 show exemplary cross sectional views corresponding to line X1-X1 of FIG. 1A, illustrating various stages of the sequential fabrication process of a semiconductor device according to one embodiment of the present disclosure. It is understood that additional operations can be provided before, during, and after processes shown by FIGS. 2-16, and some of the operations described below can be replaced or eliminated, for additional embodiments of the method. The order of the operations/processes may be interchangeable.

As shown in FIG. 2, the gate electrode layer 10 is recessed by using a dry and/or a wet etching process. The depth D1 above the gate electrode 10 of the recessed space 25 measured from the upper surface of the first ILD layer 40 is in a range from about 10 nm to about 25 nm in some embodiments, and is in a range from about 15 nm to about 20 nm in other embodiments.

As shown in FIG. 3, the sidewall spacers 30 are recessed by using a dry and/or a wet etching process to broaden the recessed space 25. Since the sidewall spacers 30 are made of a material different from the first ILD layer 40, the sidewall spacer layers 30 can be substantially selectively etched. The depth D2 above the sidewall spacers 30 of the recessed space 25 measured from the upper surface of the first ILD layer 40 is in a range from about 5 nm to about 20 nm in some embodiments, and is in a range from about 8 nm to about 15 nm in other embodiments.

The depth D2 is different from the depth D1. In some embodiments, the depth D2 is smaller than the depth D1. In other words, in FIG. 3, the top of the sidewall spacers 30 is higher than the top of the gate electrode 10. The difference between the depth D2 and the depth D1 (i.e., the difference in heights of the sidewall spacers 30 and the gate electrode 10) is in a range from about 5 nm to about 15 nm in some embodiments, and is in a range from about 8 nm to about 12 nm in other embodiments.

It is noted that the gate electrode layer 10 may be recessed after the sidewall spacers 30 are recessed.

Then, a protective layer 60 is conformally formed in the recessed space 25, as shown in FIG. 4. The protective layer 60 protects the sidewall spacers 30 from subsequent etching operations. Further, the protective layer 60 disposed above the gate electrode 10 functions as a cap insulating layer in the gate structure. One or more blanket layers of insulating material are conformally formed over the structure shown in FIG. 3. As shown in FIG. 3, the protective layer 60 partially fills the space 25. The thickness of the protective layer 60 is in a range from about 3 nm to about 5 nm in some embodiments.

After the protective layer 60 is formed, a first etch-stop layer (ESL) 70 is formed on the protective layer 60. One or more blanket layers of insulating material are formed on the protective layer 60. Then, a planarization operation, such as an etch-back process and/or a chemical mechanical polishing (CMP) process, is performed to remove the upper portions of the protective layer 60 and the first ESL 70, as shown in FIG. 6.

After the planarization operation, the first ESL 70 is in a range from about 40 nm to about 50 nm in some embodiments, and is in a range from about 20 nm to about 30 nm in other embodiments.

The protective layer 60 and the first ESL 70 are made of different insulating materials. The protective layer 60 is made of a material which has a high etching resistivity against silicon based insulating materials. In some embodiments, an aluminum based insulating material, such as AlO, AlON and/or AN, is used as the protective layer 60, and a silicon nitride based material, such as SiN and/or SiON, is used as the first ESL 70. The first ESL 70 disposed above the gate electrode 10 functions as another cap insulating layer in the gate structure.

After the planarization operation, the first ILD layer 40 disposed over the source/drain structures 50 is removed, as shown in FIG. 7 by using a suitable etching operation.

Subsequently, a conductive material is formed over the structure of FIG. 7. One or more layers of conductive material, such as tungsten, titanium, cobalt, tantalum, copper, aluminum or nickel, or silicide thereof, or other suitable materials, are formed over the structure of FIG. 7. Then, a planarization operation, such as a CMP process, is performed, so as to obtain the structure of FIG. 8. The space between two gate structures is filled by the conductive material, thereby forming a source/drain contact layer 80 in contact with the source/drain region 50.

Then, as shown in FIG. 9, the source/drain contact layer 80 is recessed by using a suitable etching operation. The spaces formed by recessing the source/drain contact layer 80 is filled with an insulating material, thereby forming a second ESL 90, as shown in FIG. 10.

The second ESL 90 includes one or more layers of a silicon carbide based insulating material, such as SiC and/or SiOC. A blanket layer of the insulating material is formed over the structure of FIG. 9, and then a planarization operation, such as CMP, is performed, thereby obtaining the structure of FIG. 10.

Further, as shown in FIG. 11, a second ILD 100 is formed over the structure of FIG. 10. The second ILD layer 100 includes one or more layers of insulating material including a silicon oxide based material, such as silicon dioxide (SiO₂) and SiON, or a low-k dielectric material. In some embodiments, a third ESL 105 made of, for example, SiN, SiON and/or SiOCN, is formed before forming the second ILD layer 100.

After forming the second ILD layer 100, a first mask pattern 110 having an opening above the gate electrode 10 is formed over the second ILD layer 100. By using the first mask pattern 110 as an etching mask, the second ILD layer 100, the third ESL 105 and the first ESL 70 are etched to form a contact hole 112, using an etching operation, as shown in FIG. 12. In this etching operation, the protective layer 60 formed on the gate electrode 10 functions as an etching-stop layer, and the etching of the first ESL 70 substantially stops at the protective layer 60. The first mask pattern 110 includes at least one of a resist pattern and a hard mask pattern. The hard mask pattern may include one or more layers of dielectric material, metal nitride, such as TiN or TaN, or metal oxide, such as TiO₂.

Subsequently, the protective layer 60 is further etched to complete the forming of the contact hole 112, as shown in FIG. 13. The etching of the protective layer 60 includes a wet etching process in some embodiments. Then, the first mask pattern 110 is removed. In some embodiments, the first mask pattern 110 is removed before the etching of the protective layer 60.

As shown in FIG. 14, a second mask pattern 115 having an opening above the source/drain contact layer 80 is formed over the second ILD layer 100. By using the second mask pattern 115 as an etching mask, the second ILD layer 100, the third ESL 105 and the second ESL 90 are etched to form a contact hole 117, using an etching operation, as shown in FIG. 14. In this etching operation, the protective layer 60 (and the sidewall spaces 30) is not substantially etched, thus the contact hole 117 can be formed in a self-aligned manner. The second mask pattern 115 includes at least one of a resist pattern and a hard mask pattern. The hard mask pattern may include one or more layers of dielectric material, metal nitride, such as TiN or TaN, or metal oxide, such as TiO₂. Then, the second mask pattern 115 is removed, as shown in FIG. 15. In some embodiments, the second mask pattern 115 is removed during the etching of the second ESL 90.

In some embodiments, the contact hole 112 is formed after the contact hole 117 is formed.

The contact holes 112 and 117 are then filed with one or more conductive materials so as to form via plugs 120 and 122, as shown in FIG. 16. A blanket layer of conductive material is formed over the structure of FIG. 15, and then a planarization operation, such as CMP, is performed.

It is understood that the device shown in FIG. 16 undergoes further CMOS processes to form various features such as interconnect metal layers, dielectric layers, passivation layers, etc.

The various embodiments or examples described herein offer several advantages over the existing art. For example, in the present disclosure, it is possible to form two cap layers over the gate electrode with simplified manufacturing operations, and the two cap layers are used as contact-etch stop layers. Further, one of the two cap layers is also used as a protective layer for the sidewall spacers, which also simplifies the manufacturing operations. By using different materials for the protective layer, the first etch-stop layers (cap layers) and the second etch-stop layer, it is possible to gain an etching selectivity during a contact hole etching operation.

It will be understood that not all advantages have been necessarily discussed herein, no particular advantage is required for all embodiments or examples, and other embodiments or examples may offer different advantages.

According to one aspect of the present disclosure, in a method of manufacturing a semiconductor device, a first gate structure and a second gate structure are formed over a substrate. The first gate structure includes a first gate electrode layer and first sidewall spacers disposed on both side faces of the first gate electrode layer, and the second gate structure includes a second gate electrode layer and second sidewall spacers disposed on both side faces of the second gate electrode layer. A first insulating layer is formed between the first gate structure and the second gate structure. After the first insulating layer is formed, the first and second gate electrode layers are recessed, and the first and second sidewall spacers are recessed, thereby forming a first space over the recessed first gate electrode layer and the recessed first sidewall spacers and a second space over the recessed gate electrode layer and the recessed second sidewall spacers. A first protective layer is conformally formed in the first space and a second protective layer is conformally formed in the second space. A first etch-stop layer is formed on the first protective layer and a second etch-stop layer is formed on the second protective layer. A first depth of the first space above the first side wall spacers is different from a second depth of the first space above the first gate electrode layer.

According to another aspect of the present disclosure, in a method of manufacturing a semiconductor device, a first gate structure and a second gate structure are formed over a substrate. The first gate structure includes a first gate electrode layer and first sidewall spacers disposed on both side faces of the first gate electrode layer, and the second gate structure includes a second gate electrode layer and second sidewall spacers disposed on both side faces of the second gate electrode layer. A first source/drain region is formed in an area between the first gate structure and the second gate structure. A first insulating layer is formed over the first source/drain region and between the first gate structure and the second gate structure. After the first insulating layer is formed, the first and second gate electrode layers are recessed, and the first and second sidewall spacers are recessed, thereby forming a first space over the recessed first gate electrode layer and the recessed first sidewall spacers and a second space over the recessed gate electrode layer and the recessed second sidewall spacers. A first protective layer is conformally formed in the first space and a second protective layer is conformally formed in the second space. A first etch-stop layer is formed on the first protective layer and a second etch-stop layer is formed on the second protective layer. The first insulating layer disposed over the first source/drain region is removed, thereby forming a source/drain space. The source/drain space is filled with a conductive material. The filled conductive material is recessed, thereby forming a source/drain contact layer. A third etch-stop layer is formed over the source/drain contact layer.

In accordance with yet another aspect of the present disclosure, a semiconductor device includes a gate structure. The gate structure include a gate electrode layer, a first cap insulating layer disposed over the gate electrode layer, a second cap insulating layer disposed over the first cap insulating layer, and first sidewall spacers disposed on both side faces of the gate electrode layer. The first cap insulating layer extends over and is disposed on the first sidewall spacers.

The foregoing outlines features of several embodiments or examples so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments or examples introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor device, comprising: a first gate structure over a channel region, the first gate structure including a first gate electrode layer, first sidewall spacers disposed on both side faces of the first gate electrode layer, and one or more first cap insulating layers disposed over the first gate electrode layer; a second gate structure over the substrate, the second gate structure including a second gate electrode layer, second sidewall spacers disposed on both side faces of the second gate electrode layer, and one or more second cap insulating layers disposed over the second gate electrode layer; a first dielectric layer disposed in which the first gate structure and the second gate structure are embedded; a first source/drain epitaxial layer disposed between the first and second gate structures, wherein a top of the first source/drain epitaxial layer is higher than a top of the channel region; a source/drain conductive plug disposed on the first source/drain epitaxial layer, wherein a lateral surface of the first source/drain conductive plug contacts a lateral surface of one of the first sidewall spacers and one of the second sidewall spacers; and a source/drain cap insulating layer disposed on the source/drain conductive plug, wherein the source/drain etch-stop plug is in direct contact with the lateral surface of the one of the first sidewall spacers and the one of the second sidewall spacers.
 2. The semiconductor device of claim 1, wherein the one or more first cap insulating layer and the one of more second cap insulating layers include silicon nitride.
 3. The semiconductor device of claim 1, wherein the source/drain conductive plug includes silicide.
 4. The semiconductor device of claim 1, wherein a top of the one or more first cap insulating layer, a top of the one of more second cap insulating layers and a top of the source/drain cap insulating layer are flush with each other.
 5. The semiconductor device of claim 1, further comprising a gate contact contacting the first gate electrode, wherein the first and second gate electrodes extend in a first direction, and in a cross section cutting the gate contact along a second direction perpendicular to the first direction, an upper surface of the second gate electrode is fully covered by the one or more second cap insulating layers.
 6. The semiconductor device of claim 1, further comprising an etch stop layer in contact with wherein a top of the one or more first cap insulating layer, a top of the one of more second cap insulating layers, a top of the source/drain cap insulating layer, and a top of the first dielectric layer.
 7. The semiconductor device of claim 6, wherein the etch stop layer includes at least one selected the group consisting of SiN, SiON and SiOCN.
 8. The semiconductor device of claim 6, further comprising a second dielectric layer disposed on the etch stop layer.
 9. A semiconductor device, comprising: a first gate structure over a fin structure, the first gate structure including a first gate electrode layer, first sidewall spacers disposed on both side faces of the first gate electrode layer, a first cap insulating layer disposed over the first gate electrode layer, and a first etch-stop-layer disposed over the first cap insulating layer; a second gate structure over the fin structure, the second gate structure including a second gate electrode layer, second sidewall spacers disposed on both side faces of the second gate electrode layer, a second cap insulating layer disposed over the second gate electrode layer, and a second etch-stop-layer disposed over the second cap insulating layer; a source/drain epitaxial layer disposed between the first and second gate structures and protruding from the fin structure; a source/drain conductive plug disposed on the source/drain epitaxial layer, wherein a lateral surface of the source/drain conductive plug contacts a lateral surface of one of the first sidewall spacers and one of the second sidewall spacers; and a source/drain etch-stop plug disposed on the first source/drain conductive plug, wherein the source/drain etch-stop plug is in direct contact with the lateral surface of the one of the first sidewall spacers and the one of the second sidewall spacers and is in direct contact with a lateral surface of the first cap insulating layer.
 10. The semiconductor device of claim 9, wherein the first cap insulating layer is made of a different material than the second cap insulating layer.
 11. The semiconductor device of claim 10, wherein the first cap insulating layer is made of an aluminum based insulating material.
 12. The semiconductor device of claim 10, wherein the second cap insulating layer is made of a silicon nitride based insulating material.
 13. The semiconductor device of claim 10, further comprising: a first dielectric layer disposed between the first gate structure and the second gate structure; a third etch-stop-layer disposed on and in direct contact with the first cap insulating layer, the first etch-stop-layer, the second cap insulating layer, the second etch-stop-layer and the first dielectric layer; and a second dielectric layer disposed on the third etch-stop-layer.
 14. The semiconductor device of claim 13, wherein the third etch-stop-layer is made of a different material than the first and second cap insulating layers.
 15. The semiconductor device of claim 14, wherein the third-stop-layer is made of at least one selected the group consisting of SiN, SiON and SiOCN.
 16. The semiconductor device of claim 10, wherein the source/drain etch-stop plug is made of at least one selected the group consisting of SiC and SiOC.
 17. A semiconductor device, comprising: a first gate structure over a fin structure, the first gate structure including a first gate electrode layer, first sidewall spacers disposed on both side faces of the first gate electrode layer, a first cap insulating layer disposed over the first gate electrode layer, and a first etch-stop-layer disposed over the first cap insulating layer; a second gate structure over the fin structure, the second gate structure including a second gate electrode layer, second sidewall spacers disposed on both side faces of the second gate electrode layer, a second cap insulating layer disposed over the second gate electrode layer, and a second etch-stop-layer disposed over the second cap insulating layer; a third gate structure over the fin structure, the third gate structure including a third gate electrode layer, third sidewall spacers disposed on both side faces of the third gate electrode layer, a third cap insulating layer disposed over the third gate electrode layer, and a third etch-stop-layer disposed over the third cap insulating layer; a first source/drain epitaxial layer disposed between the first and second gate structures and protruding from the fin structure; a first source/drain conductive plug disposed on the first source/drain epitaxial layer, wherein a lateral surface of the source/drain conductive plug contacts a lateral surface of one of the first sidewall spacers and one of the second sidewall spacers; a second source/drain epitaxial layer disposed between the second and third gate structures and protruding from the fin structure; a second source/drain conductive plug disposed on the second source/drain epitaxial layer, wherein a lateral surface of the source/drain conductive plug contacts a lateral surface of one of the second sidewall spacers and one of the third sidewall spacers; and a source/drain etch-stop plug disposed on the first source/drain conductive plug; and a source/drain contact contacting the second source/drain conductive plug.
 18. The semiconductor device of claim 17, wherein the source/drain etch-stop plug is in direct contact with the lateral surface of the one of the first sidewall spacers and the one of the second sidewall spacers and is in direct contact with a lateral surface of the first cap insulating layer and a lateral surface of the second cap insulating layer.
 19. The semiconductor device of claim 17, wherein the source/drain contact is in direct contact with the lateral surface of the one of the second sidewall spacers and the one of the third sidewall spacers and is in direct contact with a lateral surface of the second cap insulating layer and a lateral surface of the third cap insulating layer.
 20. The semiconductor device of claim 17, wherein: a thickness of a part of the first cap insulating layer disposed over the first sidewall spacers is greater than a thickness of a part of the first cap insulating layer covering an upper surface of the first gate electrode, and the thickness of the part of the first cap insulating layer covering the upper surface of the first gate electrode is smaller than a thickness of the second cap insulating layer over the gate electrode. 